Camera Tracking - Nuke 101: Professional Compositing and Visual Effects - page 432

10. Right-click (Ctrl-click) in the 2D Viewer. From the contextual menu choose
Ground Plane, then Set X.
This sets the table so it's roughly on the X and Z axes of the world space, which
will help you later in placing things in the world. The important thing is that the
table is now flat and horizontal ( FIGURE 10.24 ) .
Figure 10.24. Notice the points representing the table are now parallel to the
3D Viewer's grid.
The realignment is complete. Let's tidy up the screen.
11. Choose Restore Layout 1 from the Layout menu in the menu bar.